/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.core;

import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.lang.reflect.WildcardType;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.ConcurrentReferenceHashMap;

/**
 * Helper class for resolving generic types against type variables.
 *
 * <p>Mainly intended for usage within the framework, resolving method
 * parameter types even when they are declared generically.
 *
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @author Sam Brannen
 * @author Phillip Webb
 * @since 2.5.2
 */
public abstract class GenericTypeResolver {

    /**
     * Cache from Class to TypeVariable Map
     */
    @SuppressWarnings("rawtypes")
    private static final Map<Class<?>, Map<TypeVariable, Type>> typeVariableCache = new ConcurrentReferenceHashMap<>();


    /**
     * Determine the target type for the given generic parameter type.
     *
     * @param methodParameter     the method parameter specification
     * @param implementationClass the class to resolve type variables against
     * @return the corresponding generic parameter or return type
     */
    public static Class<?> resolveParameterType(MethodParameter methodParameter, Class<?> implementationClass) {
        Assert.notNull(methodParameter, "MethodParameter must not be null");
        Assert.notNull(implementationClass, "Class must not be null");
        methodParameter.setContainingClass(implementationClass);
        ResolvableType.resolveMethodParameter(methodParameter);
        return methodParameter.getParameterType();
    }

    /**
     * Determine the target type for the generic return type of the given method,
     * where formal type variables are declared on the given class.
     *
     * @param method the method to introspect
     * @param clazz  the class to resolve type variables against
     * @return the corresponding generic parameter or return type
     */
    public static Class<?> resolveReturnType(Method method, Class<?> clazz) {
        Assert.notNull(method, "Method must not be null");
        Assert.notNull(clazz, "Class must not be null");
        return ResolvableType.forMethodReturnType(method, clazz).resolve(method.getReturnType());
    }

    /**
     * Resolve the single type argument of the given generic interface against the given
     * target method which is assumed to return the given interface or an implementation
     * of it.
     *
     * @param method     the target method to check the return type of
     * @param genericIfc the generic interface or superclass to resolve the type argument from
     * @return the resolved parameter type of the method return type, or {@code null}
     * if not resolvable or if the single argument is of type {@link WildcardType}.
     */
    @Nullable
    public static Class<?> resolveReturnTypeArgument(Method method, Class<?> genericIfc) {
        Assert.notNull(method, "method must not be null");
        ResolvableType resolvableType = ResolvableType.forMethodReturnType(method).as(genericIfc);
        if (!resolvableType.hasGenerics() || resolvableType.getType() instanceof WildcardType) {
            return null;
        }
        return getSingleGeneric(resolvableType);
    }

    /**
     * Resolve the single type argument of the given generic interface against
     * the given target class which is assumed to implement the generic interface
     * and possibly declare a concrete type for its type variable.
     *
     * @param clazz      the target class to check against
     * @param genericIfc the generic interface or superclass to resolve the type argument from
     * @return the resolved type of the argument, or {@code null} if not resolvable
     */
    @Nullable
    public static Class<?> resolveTypeArgument(Class<?> clazz, Class<?> genericIfc) {
        ResolvableType resolvableType = ResolvableType.forClass(clazz).as(genericIfc);
        if (!resolvableType.hasGenerics()) {
            return null;
        }
        return getSingleGeneric(resolvableType);
    }

    @Nullable
    private static Class<?> getSingleGeneric(ResolvableType resolvableType) {
        Assert.isTrue(resolvableType.getGenerics().length == 1,
                () -> "Expected 1 type argument on generic interface [" + resolvableType +
                        "] but found " + resolvableType.getGenerics().length);
        return resolvableType.getGeneric().resolve();
    }


    /**
     * Resolve the type arguments of the given generic interface against the given
     * target class which is assumed to implement the generic interface and possibly
     * declare concrete types for its type variables.
     *
     * @param clazz      the target class to check against
     * @param genericIfc the generic interface or superclass to resolve the type argument from
     * @return the resolved type of each argument, with the array size matching the
     * number of actual type arguments, or {@code null} if not resolvable
     */
    @Nullable
    public static Class<?>[] resolveTypeArguments(Class<?> clazz, Class<?> genericIfc) {
        ResolvableType type = ResolvableType.forClass(clazz).as(genericIfc);
        if (!type.hasGenerics() || type.isEntirelyUnresolvable()) {
            return null;
        }
        return type.resolveGenerics(Object.class);
    }

    /**
     * Resolve the given generic type against the given context class,
     * substituting type variables as far as possible.
     *
     * @param genericType  the (potentially) generic type
     * @param contextClass a context class for the target type, for example a class
     *                     in which the target type appears in a method signature (can be {@code null})
     * @return the resolved type (possibly the given generic type as-is)
     * @since 5.0
     */
    public static Type resolveType(Type genericType, @Nullable Class<?> contextClass) {
        if (contextClass != null) {
            if (genericType instanceof TypeVariable) {
                ResolvableType resolvedTypeVariable = resolveVariable(
                        (TypeVariable<?>) genericType, ResolvableType.forClass(contextClass));
                if (resolvedTypeVariable != ResolvableType.NONE) {
                    Class<?> resolved = resolvedTypeVariable.resolve();
                    if (resolved != null) {
                        return resolved;
                    }
                }
            } else if (genericType instanceof ParameterizedType) {
                ResolvableType resolvedType = ResolvableType.forType(genericType);
                if (resolvedType.hasUnresolvableGenerics()) {
                    ParameterizedType parameterizedType = (ParameterizedType) genericType;
                    Class<?>[] generics = new Class<?>[parameterizedType.getActualTypeArguments().length];
                    Type[] typeArguments = parameterizedType.getActualTypeArguments();
                    for (int i = 0; i < typeArguments.length; i++) {
                        Type typeArgument = typeArguments[i];
                        if (typeArgument instanceof TypeVariable) {
                            ResolvableType resolvedTypeArgument = resolveVariable(
                                    (TypeVariable<?>) typeArgument, ResolvableType.forClass(contextClass));
                            if (resolvedTypeArgument != ResolvableType.NONE) {
                                generics[i] = resolvedTypeArgument.resolve();
                            } else {
                                generics[i] = ResolvableType.forType(typeArgument).resolve();
                            }
                        } else {
                            generics[i] = ResolvableType.forType(typeArgument).resolve();
                        }
                    }
                    Class<?> rawClass = resolvedType.getRawClass();
                    if (rawClass != null) {
                        return ResolvableType.forClassWithGenerics(rawClass, generics).getType();
                    }
                }
            }
        }
        return genericType;
    }

    private static ResolvableType resolveVariable(TypeVariable<?> typeVariable, ResolvableType contextType) {
        ResolvableType resolvedType;
        if (contextType.hasGenerics()) {
            resolvedType = ResolvableType.forType(typeVariable, contextType);
            if (resolvedType.resolve() != null) {
                return resolvedType;
            }
        }

        ResolvableType superType = contextType.getSuperType();
        if (superType != ResolvableType.NONE) {
            resolvedType = resolveVariable(typeVariable, superType);
            if (resolvedType.resolve() != null) {
                return resolvedType;
            }
        }
        for (ResolvableType ifc : contextType.getInterfaces()) {
            resolvedType = resolveVariable(typeVariable, ifc);
            if (resolvedType.resolve() != null) {
                return resolvedType;
            }
        }
        return ResolvableType.NONE;
    }

    /**
     * Resolve the specified generic type against the given TypeVariable map.
     * <p>Used by Spring Data.
     *
     * @param genericType the generic type to resolve
     * @param map         the TypeVariable Map to resolved against
     * @return the type if it resolves to a Class, or {@code Object.class} otherwise
     */
    @SuppressWarnings("rawtypes")
    public static Class<?> resolveType(Type genericType, Map<TypeVariable, Type> map) {
        return ResolvableType.forType(genericType, new TypeVariableMapVariableResolver(map)).resolve(Object.class);
    }

    /**
     * Build a mapping of {@link TypeVariable#getName TypeVariable names} to
     * {@link Class concrete classes} for the specified {@link Class}.
     * Searches all super types, enclosing types and interfaces.
     *
     * @see #resolveType(Type, Map)
     */
    @SuppressWarnings("rawtypes")
    public static Map<TypeVariable, Type> getTypeVariableMap(Class<?> clazz) {
        Map<TypeVariable, Type> typeVariableMap = typeVariableCache.get(clazz);
        if (typeVariableMap == null) {
            typeVariableMap = new HashMap<>();
            buildTypeVariableMap(ResolvableType.forClass(clazz), typeVariableMap);
            typeVariableCache.put(clazz, Collections.unmodifiableMap(typeVariableMap));
        }
        return typeVariableMap;
    }

    @SuppressWarnings("rawtypes")
    private static void buildTypeVariableMap(ResolvableType type, Map<TypeVariable, Type> typeVariableMap) {
        if (type != ResolvableType.NONE) {
            Class<?> resolved = type.resolve();
            if (resolved != null && type.getType() instanceof ParameterizedType) {
                TypeVariable<?>[] variables = resolved.getTypeParameters();
                for (int i = 0; i < variables.length; i++) {
                    ResolvableType generic = type.getGeneric(i);
                    while (generic.getType() instanceof TypeVariable<?>) {
                        generic = generic.resolveType();
                    }
                    if (generic != ResolvableType.NONE) {
                        typeVariableMap.put(variables[i], generic.getType());
                    }
                }
            }
            buildTypeVariableMap(type.getSuperType(), typeVariableMap);
            for (ResolvableType interfaceType : type.getInterfaces()) {
                buildTypeVariableMap(interfaceType, typeVariableMap);
            }
            if (resolved != null && resolved.isMemberClass()) {
                buildTypeVariableMap(ResolvableType.forClass(resolved.getEnclosingClass()), typeVariableMap);
            }
        }
    }


    @SuppressWarnings({"serial", "rawtypes"})
    private static class TypeVariableMapVariableResolver implements ResolvableType.VariableResolver {

        private final Map<TypeVariable, Type> typeVariableMap;

        public TypeVariableMapVariableResolver(Map<TypeVariable, Type> typeVariableMap) {
            this.typeVariableMap = typeVariableMap;
        }

        @Override
        @Nullable
        public ResolvableType resolveVariable(TypeVariable<?> variable) {
            Type type = this.typeVariableMap.get(variable);
            return (type != null ? ResolvableType.forType(type) : null);
        }

        @Override
        public Object getSource() {
            return this.typeVariableMap;
        }
    }

}
